A messy multibillion-dollar weapon sale between Turkey, Russia and the US just got more complicated

Russia's S-400, a mobile long-range surface-to-air missile system, cannot be operated alongside the Patriot system or the F-35.

The Kremlin says it will press ahead with delivering the S-400 to Ankara despite the possible sale of the Patriot system.

An S-400 Triumf surface-to-air missile system seen in St. Petersburg's Palace Square during a dress rehearsal for a military parade.

Peter Kovalev | TASS via Getty Images

WASHINGTON — Russia will deliver its S-400 missile defense system to Turkey despite the U.S. State Department's decision to sell a rival platform to Ankara for $3.5 billion.

The S-400, a mobile long-range surface-to-air missile system, is the Kremlin's answer to America's Patriot and THAAD platforms. Lockheed Martin makes the THAAD, or terminal high altitude area defense, system, while Raytheon makes the Patriot.

Last year, Ankara signed an agreement with Moscow for the S-400 missile system, a deal reportedly worth $2.5 billion. All the while, Turkey has helped finance America's most expensive weapons system, the F-35 Joint Strike Fighter.

In short, these two big-ticket weapons systems that Turkey hopes to add to its budding arsenal can be used against each other.

An F-35 fighter jet is seen as Turkey takes delivery of its first F-35 fighter jet with a ceremony in Forth Worth, Texas, USA on June 21, 2018. Two such planes destined for Turkey are yet to leave American soil.

Atilgan Ozdil | Anadolu Agency | Getty Images

The Russian-made S-400 missile system, which is equipped with eight launchers and 32 missiles, is capable of targeting stealth warplanes like the F-35 fighter.

Turkey's march toward procuring the Russian missile system has raised concerns among its fellow NATO members and Washington, who are wary of Moscow's increasing military presence in the region. Meanwhile, Congress has pushed back on the scheduled transfer of two F-35 jets to Turkey.

Kremlin spokesman Dmitry Peskov said that the Russian and U.S. transactions should be seen as separate from each other, and that Moscow was in the process of supplying Ankara with the S-400.

"We are fulfilling agreements that we have with our Turkish colleagues. You know that the contract is being fulfilled. This will be continued," Peskov told reporters Wednesday.

A Russian S-400 surface-to-air missile system.

Sergei Malgavko | TASS via Getty Images

What's more, the State Department approved a proposed sale of the Patriot missile defense system to Ankara on Tuesday.

"This sale is consistent with U.S. initiatives to provide key allies with modern systems capable of being networked to defend against regional instability," a State Department spokesperson, who was not authorized to speak publicly, said ahead of the announcement.

The potential sale of the Patriot system complicates Russia's sale of the S-400 to Turkey since the two missile systems cannot be operated together. Additionally, the F-35 jets that Turkey also hopes to buy cannot be operated in conjunction with the S-400.

"Turkey cannot buy both," Tim Ash, a senior emerging markets strategist at Bluebay Asset Management, said of the development. "I think the U.S. will pull both the Patriot sale and F-35 deal if Turkey goes along with the S-400," he added.

"Net-net, I think the news about Patriot is still a positive, as it shows the U.S. and Turkey are talking and moving back closer together. That said, the Turks might be trying to drive too hard a bargain, and might end up with nothing as a result."

Turkey said last month that its purchase of the Russian missiles was a done deal and could not be canceled, according to a Reuters report. Ankara said it needed to buy further defense hardware however, which could be bought from the United States, the report said.

In this handout image provided by the German Bundeswehr armed forces a patriot missile Raytheon MIN-104 is seen during the Battle Griffin 2005 excersise on February 25, 2005 in Bodo, Norway.